This study aimed to examine whether there is a mediating role of emotion regulation difficulties in the relationship between social anxiety and problematic Internet use (PIU). The sample consisted of 297 participants (147 [49%] males; aged from 18 to 24 years), who were university students studying sport sciences in four universities in Turkey. Data were obtained using the Liebowitz Social Anxiety Scale, Internet Addiction Scale, and Scale of Difficulties in Emotional Regulation. Structural Equation Modeling (SEM) was used to analyze the data. According to the results obtained, emotion regulation difficulty has a full mediating role in the relationship between social anxiety and PIU. As a result, social anxiety affects emotion regulation difficulties and this effect could increase PIU.